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Appendix II.

forittleness. The steel cylinders now used for storing compressed
gases are thus made in one piece; so also are boiler tubes and
•cartridge cases. The last-mentioned have become of large size
since the introduction of the quick-firing gun, and very heavy
presses are therefore employed, the operations at Woolwich in
•drawing such a case for a 6 in. quick-firing gun being shewn in
Fig. 770, as described by Sir William Anderson before the
Institution of Mechanical Engineers in 1897.

Metal-spinning is a method of moulding thin flexible metal
•sheets upon wood blocks fixed in a lathe chuck, by means of
a wooden tool or presser. In this manner knobs, teapots, and
many other domestic articles can be built from spun hemispheres
or saucers.


P. 152. Lathe Centres.—The American practice is to use
an angle of 60° for work up to 15 ins. diameter (7Jin. centres),




and 70° to 90° when above that diameter. Mr. W. H. Pretty,
Wh. Sc., of Bedford, writes that an endeavour there to use 75°
for small work (up to f cwt.), and 80° for larger work, met with
failure through changing ! of work, and a general standard of 80°
being first adopted, was afterwards altered to 60° to suit American
tools. For work above f cwt he drills the ends with brace and
bits, as in Fig. 771, by placing it on supports in line with lathe